Use keystone.common.provider_api for policy APIs
Use keystone.common.provider_api for policy APIs

This change converts the usage of self.<provider_api> to
keystone.common.providers_api.ProviderAPIs.<provider_api> in manager
and controller logic. This is the correct way to reference
providers from other managers and controllers now that dependency
injection has been eliminated.

Change-Id: Ieea66d86d6d28ac105c4c39bdea1d05aec8e0c46

openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone,mahak/keystone,openstack/keystone